In recent years, new energy-production techniques have attracted attention from the standpoint of environmental issues, and among these techniques a fuel cell has attracted particular interest. The fuel cell converts chemical energy to electric energy through electrochemical reaction of hydrogen and oxygen, attaining high energy utilization efficiency. Therefore, extensive studies have been carried out on realization of fuel cells for public use, industrial use, automobile use, etc.
Fuel cells are categorized in accordance with the type of employed electrolyte, and, among others, a phosphoric acid type, a molten carbonate salt type, a solid oxide type, and a polymer electrolyte type have been known. With regard to hydrogen sources, studies have been conducted on methanol; liquefied natural gas predominantly containing methane; city gas predominantly containing natural gas; a synthetic liquid fuel produced from natural gas serving as a feedstock; and petroleum-derived hydrocarbons such as naphtha and kerosene.
When hydrogen is produced from petroleum-derived hydrocarbons, the hydrocarbons are generally steam-reformed in the presence of a catalyst. Among such catalysts, catalysts that contain ruthenium supported on a carrier as an active component have conventionally been studied, in view of their advantages; e.g., comparatively high activity and suppression of carbon deposition even under low steam/carbon ratio operational conditions. In recent years, these ruthenium catalysts have been envisaged for use in fuel cells, which require a long-life catalyst.
Since the discovery of a co-catalyst effect of cerium oxide or zirconium oxide exerted on a ruthenium catalyst, ruthenium-cerium oxide-based and ruthenium-zirconium oxide-based catalysts have been studied and some patent applications have been filed. In addition to ruthenium-based catalysts, catalysts based on a platinum component, a rhodium component, a palladium component, an iridium component, or a nickel component have been studied. However, these catalysts have drawbacks, in that catalytic activity in terms of steam reforming of hydrocarbons remains unsatisfactory, and that carbon is deposited in a large amount during reforming.
In addition to the aforementioned steam reforming, other reforming processes for producing hydrogen, such as autothermal reforming, partial-oxidation reforming, and carbon dioxide reforming have been studied. As is known, all the above reforming processes can generally be performed through employment of the same reforming catalyst, and with slight modification of reforming conditions, all the above processes can also produce synthesis gas. Studies have also been carried out on use of components such as a ruthenium component, a platinum component, a rhodium component, a palladium component, an iridium component, and a nickel component in catalysts for the above autothermal reforming, partial-oxidation reforming, and carbon dioxide reforming. However, catalytic activity of the catalyst employing the elements remains unsatisfactory.
There have been proposed an enhanced-activity hydrocarbon reforming catalyst comprising a carrier containing manganese oxide and, supported on the carrier, at least one component selected from among a ruthenium component, a platinum component, a rhodium component, a palladium component, an iridium component, and a nickel component; a method for producing the reforming catalyst; and methods of the steam reforming, autothermal reforming, partial-oxidation reforming, and carbon dioxide reforming of hydrocarbon by use of the reforming catalyst (Patent Document 1).
There have been proposed a hydrocarbon reforming catalyst which is produced by preparing a catalyst comprising a carrier containing manganese oxide and, supported on the carrier, at least one component selected from among a ruthenium component, a platinum component, a rhodium component, a palladium component, an iridium component, and a nickel component, by use of at least one chlorine-containing compound; decomposing the compound with an aqueous alkaline solution, and removing chlorine atoms through washing with water; a method for producing the catalyst; and a hydrocarbon reforming method employing the reforming catalyst (Patent Document 2). However, the above disclosed reforming catalysts, exhibiting high activity in terms of reforming reaction, have problematically poor durability; i.e., poor strength, particularly compressive strength.
Patent Document 1
Pamphlet of International Patent Application No. 02/078840
Patent Document 2
Japanese Patent Application Laid-Open (kokai) No. 2003-265963